The dichotomous key illustrated here allows the classification of microorganisms based on their metabolic characteristics. suppose some organisms ferment lactose but can't use citric acid for all their carbon needs. these organisms must be

The organism must be Escherichia coli

Escherichia coli is a bacterium of the family Enterobacteriaceae.

Escherichia coli is abundant in the commensal flora, particularly in the digestive tract.

Aerobic bacillus, Gram negative, oxidase negative, nitrate positive and which ferments glucose.

* fermentation of sugars: glucose +, lactose +

* reduction of nitrates to nitrites: NO3 +

* metabolism of tryptophan to indole: ind +

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.